The trend to ever-increasing vehicle quality and tighter quality control in automotive vehicle and vehicle parts production continues unabated. Quality standards set but a decade ago have long since been abandoned as inadequate. Current standards are set not only with regard to the overall design of vehicles, but also to workmanship considerations such as fit and finish.
Flaws in paint finish, such as pits, dimples or discolouration may arise from underlying flaws in the metal surface of the vehicle part or assembly, or from excess moisture left on the subject part or assembly after it undergoes one or more liquid baths prior to application of the final finishing coats of paint. The now common use of so-called "clear-coat" finishes (incorporating a clear, pigment-less top coat of lacquer applied after other finish layers) only serves to exacerbate the problem by exaggerating any underlying flaws.
In order to increase efficiency on automotive parts production lines, it has, in recent years, become increasingly common to attempt to detect the surface flaws in parts or assemblies to be painted before they are actually painted. Substantial increases in efficiency can be realized if parts or assemblies-are identified as defective in their surface finish (but profitably salvageable), prior to final painting, so that such parts can be diverted for remedial surface preparation and then re-introduced into the production line. If surface flaws on the parts and/or assemblies are not detected until after final painting, then in order to effect salvage, the newly applied paint must be completely removed before carrying out remedial surface preparation to correct flaws. This paint removal step requires the expenditure of additional time and resources, thus potentially rendering salvage of the parts and/or assemblies unprofitable.
A process generally known as "highlighting" is now commonly used to detect surface flaws just prior to the entry of the part/assembly into the paint booth for final finishing. Highlighting involves the application of a water-based photoreflective liquid to the surface of the workpiece to be painted, and thereafter the viewing of the workpiece, at a preferred angle, in light of a preferred wavelength. This process has the effect of enhancing or "highlighting" any flaws in the surface of the workpiece prior to its being painted. Parts and/or assemblies having surface defects can then be diverted for remedial refinishing. Parts and/or assemblies which show no defects while passing through the highlighting unit continue on along the production line toward the paint booth for final finishing. The water-based highlighting chemical is typically washed off or otherwise removed by other processes from the part/assembly prior to application of the final finish(es) in the paint booth.
The use of a highlighting operation interposed between the final chemical bath and the paint booth dramatically reduces the number of finished parts/assemblies which are ultimately rejected due to surface finishing flaws. The benefits to be derived in using a highlighting process to detect surface irregularities, as described above, have been generally recognized and accepted by the automotive industry. Nevertheless, certain shortcomings and problems in the highlighting process exist. For example, the highlighting chemical is typically applied by cloth or conventional brushes dragged across the surface of the part/assembly to be viewed. This application technique may result in brush patterns or lint particles being left on the workpiece, both of which interfere with the viewing of the workpiece under directed light of a selected wavelength. Accordingly, there is a potential for the introduction of further workpiece rejections as an artifact of the highlighting process. In theory, one could use conventional finishing spray equipment (as used in the application of the final paint coatings) to apply highlighting liquid, thus ensuring an excellent, even distribution of highlighting liquid. This technique is not, however, an acceptable application means for several reasons. Firstly, finishing spray equipment is quite costly, typically requiring robotics to evenly reach all surfaces of all but the simplest parts/assemblies. Secondly, such equipment requires relatively large amounts of floor space in assembly plants, which additional space is not generally available, or is too costly to provide, for allocation to a nonessential, salvaging function. Thirdly, such conventional spraying equipment for liquid coatings typically requires, for environmental and worker safety reasons, a spray booth to contain the relatively large amounts of "overspray" that they produce. The use of additional spray booths also introduces unacceptably high levels of cost and space allocation. For these reasons, conventional spray painting equipment has not found any significant degree of acceptance as a means for applying highlighting liquids to automotive parts/assemblies.
It is, therefore, an object of the present invention to provide a novel form of liquid spray nozzle which overcomes these and other problems associated with present means available for applying highlighting chemicals to, for example, automotive parts or assemblies.
More specifically it is an object of the present invention to provide a form of spray nozzle which provides for the application of a liquid to a surface in a fine aerosol form without leaving streaks or other patterns in the liquid so applied.
It is a further object of the present invention to provide a form of spray nozzle which provides for the application of a liquid to a surface in a fine aerosol form without leaving lint in the liquid so applied.
It is a further object of the present invention to provide a form of spray nozzle which provides for the directed application of a liquid to a surface to be coated in a fine aerosol spray with a minimum amount of overspray.
It is yet a further object of the present invention to provide a form of spray nozzle which provides for the directed application of a liquid to a surface to be coated in a fine aerosol spray with a minimum amount of overspray in a cost effective manner when compared to conventional spray painting equipment.
It is a further object of the present invention to provide a liquid spray nozzle which can be incorporated with other similar nozzles into a spray application system to provide for the substantially complete and uniform coverage of an object, having a large and complex surface shape, with a minimum amount of overspray and without the need for robotics.
It is a further object of the present invention to provide such a spray application system which requires a relatively small amount of floor space when compared to conventional spray painting equipment.